The present invention relates to helical scanning magnetic recording and reproduction and, more particularly, to a magnetic recording and reproduction system capable of recording the audio signal with rotary magnetic heads on slant tracks of a magnetic tape where the video signal is recorded on a multiplex basis.
In the helical scanning magnetic recording and reproduction system represented by video tape recorders and video cassette recorders, the video signal is recorded by the rotary heads on the recording medium, i.e., magnetic tape, in the form of tracks traversing askew the tape. In such recorders, the audio signal is generally recorded and reproduced on a separate track extending along the longitudinal direction of the tape by using a fixed magnetic head. FIG. 1 shows an example of these tracks formed on the magnetic tape by such a system. In the figure, reference number 1 denotes a track for recording the video signal, 2 is a track for recording the audio signal, and 3 is a magnetic tape. The figure shows the concept of recording tracks, and their dimensional relationship is not shown accurately. Other tracks such as for the control signals are omitted in the figure.
In household magnetic recording and reproduction apparatus, in particular, recording tracks for the video signal are made as narrow as possible without provision of a guard band between adjoining tracks so as to increase the recording density. On this account, the tape is fed at a very low speed. In order to further increase the recording density, many commercialized models have a "triple" recording mode in which the tape is recorded and reproduced at a speed 1/3 the standard tape speed so as to achieve the recording period three times as long as that in the normal operation mode using the same tape. In the case of a video cassette recorder handling NTSC signals of a "VHS" system, for example, the tape speed is 11 mm/sec in the dense recording mode. Such a low tape speed, however, does, not provide frequency characteristics sufficient to produce satisfactory sound quality through the recording and reproduction of the audio signal with a fixed magnetic head.
There has been proposed a method of tape recording and reproduction at a low tape speed, in which the audio signal is frequency modulated, for example, and recorded on a multiplex basis with the video signal by employment of rotary magnetic heads which provide a sufficient relative speed between each head and the recording medium. One feasible way to achieve high quality sound reproduction in triple density mode at a low tape speed is the application of the above-mentioned technique to household video cassette recorder of, for example, the "VHS" system.
However, in application of a new recording system to the prevailing magnetic recording and reproduction apparatus such as those of "VHS" system, compatibility must be retained for the reproduction of signals other than newly arranged audio signals. Therefore, the frequency spectra of the recording signal can not be changed. In addition, the above-mentioned multiplexing of the audio and video signals was not taken into account in the establishment stage of the "VHS" system, and therefore, the frequency modulated audio signal can not simply be multiplexed with the video signal.